When my engine temperature hits about 190 degrees my front brakes start to drag. As the temperature goes up they drag harder. At about 210 degrees I dont need to push the brake peddle to stop for red lights. The car comes to a pretty quick stop as soon as I push the clutch in. Interestingly, when the engine is hot and the brakes are draggin the brake peddle is very very very firm (one little tap and the brakes almost lock). As the engine cools the brakes drag less and the peddle softens up.
About a year ago I converted my front drum brakes to disc using one of those all-in-one brake conversion kits. For the first 6-7 months everything worked fine and I was very happy with the disc brakes! However, at about month 8 I noticed the drag. I discounted it at first because as soon as the car cooled off a little bit the brakes stopped dragging. Honestly, I though it was my imagination. However, the problem has grown progressively worse. I have bled and re-bled the brake lines thinking that perhaps there was an air bubble in there that was expanding with temperature but that didnt seem to help. The master cylinder is relatively new. I upgraded it when I converted the brakes.
Any other ideas out there? I would appreciate any thoughts or ideas very much as I am kinda stumped!
I had an issue with my 90 Wrangler front disc calipers hanging the caliper piston up when I used them for an aggressive stop. Pull the calipers and use a c-clamp to push back in the piston then have someone GENTLY apply the brakes to see if the piston is getting caught in the housing or seal.
Did your new master cylinder have a metal rod that fit in the master cylinder between the booster and master cylinder? If so, I have found these to be a hair too long, essentially pre-loading the brakes. What makes it worse is that every time you press the brakes the master cylinder is not fully returning to the resting position so it’s constantly retaining more pressure. The heating up and expanding of everything under the hood doesn't help either. To test this, drive the car and get it hot like you described and immediately (once home) back off the two nuts that secure the master cylinder to the booster jack up the front of the car and spin the a wheel. If the brakes loosen up you found your problem. If so just grind a little, like .050 to .075, off the rod to gain a little clearance.
Could it be that as you drive and the pads get hot from rubbing, at the same time as the engine temps, that they expand and drag worse? If it's not the pushrod maybe it's just the material the pads are made from.
My drum brakes are doing the same thing. As I explained the issue to an older mechanic last night he immediately told me it was the front rubber brake lines. He said that the interior lining of the hose had deteriorated and when hot the pieces block brake fluid from returning to the master. I'll try replacing next week.
Quick68, you hit the nail on the head. I finally found a couple hours to play so I took the firebird out and ran it around until I got to about 190 degrees and the brakes started dragging, loosened the nuts that connect the master cylinder to the booster and presto! no more dragging. I ended up taking the master cylinder off and placing washers between the master and the booster to get an idea of how much I needed to shave off the piston. I ended up needing about 0.1. I havent shaved the piston yet (ran out of time) but that is next!
Thanks the great help. As always. Firstgen is the place to go for for helpful hints!
he didnt mean shave the piston, you need to shorten the rod from the pedal to the master cyl/booster a little. I had to do the same thing , actually my "kit" came with 2 different length rods. It stated you MAY need to grind down the rod some , for the very reason your speaking of.
ok. Thanks for the clarafication. I was wondering how I was going to get in there. Does it matter which end I shave? I dont know why it would matter but it doesnt hurt to check.
Glad you found the problem! Take the rod out and inspect. If I recall correctly there is only one end that you want to grind, the other is tapered or something. you want to work on one end only anyway to help keep square. My master cylinder and booster were ordered together but didn't have any instructions about modifying that rod. Seems like they should figure the correct length ahead of time. Mine did have two rods but they were very different in length, obviously for a different application. In any case, now you can fix it and enjoy your new brakes. I used an angle grinder with a thin disc, held the rod perpendicularly and rotated it while grinding. Just go slow a make sure you have something to measure it with like dial calipars. Take a little at a time and sneak up on it, obviously if you take too much you can't put it back. After you've got it shortened just barely chamfer the edge to remove any burrs. Good luck!
ditto on the rods that came with my kit the rods were really different in length. One is for a deeper cupped master cyl and the other was for the master cyl that just basically has a small dimple for the rod. grind off metel from the end that goes ito the master cyl. thats what my instructions said.
